1. Field of the Invention
The present invention relates to an engine valve control device applied to an engine valve control mechanism that adjusts opening-closing timings of an exhaust valve or an intake valve (engine valve) of an internal combustion engine.
2. Description of Related Art
Generally, an engine valve control mechanism that adjusts opening-closing timings of an engine valve includes a hydraulic actuator that varies a rotation phase of a camshaft with respect to a crankshaft, a control valve that controls a flow of hydraulic oil supplied to the hydraulic actuator, and an electromagnetic solenoid that controls an operation of the control valve according to a control command value.
For example, according to a calculation method of the control command value described in Patent document 1 (JP-A-2007-309265), a current value applied to the electromagnetic solenoid when a deviation between an actual rotation phase (actual phase) and a target phase does not change largely but is stable is stored as a holding value, first. Then, a feedback correction value calculated from the deviation is added to the holding value to calculate the control command value. When the deviation occurs steadily, the holding value is corrected in accordance with the steady-state deviation occurring steadily, thereby storing and updating (i.e., learning) the holding value.
When temperature of the hydraulic oil is low, the viscosity of the hydraulic oil increases, so response speed of the hydraulic actuator with respect to change in the control command value lowers. That is, response speed of the actual phase with respect to change of the target phase becomes slow.
Therefore, when the actual phase is changing gradually toward the target phase because of such the low temperature, there is a possibility that it is determined that the steady-state deviation is occurring. In such the case, the holding value is corrected according to the steady-state deviation and the holding value is stored and updated (i.e., learned). Moreover, the steady-state deviation cannot be canceled by correcting the holding value only once when the temperature is low. Therefore, the holding value is corrected multiple times, thereby causing excessive correction.
If the control command value is calculated based on the holding value corrected excessively in this way and the control valve is controlled, there occurs a concern that the actual phase hunts largely with respect to the target phase.